Which came first: The Cat in The Hat or the hat on the cat? It's not clear, but we do know that Theodor Geisel -- Dr. Seuss -- loved hats. The sillier, the better:

He collected hundreds of them, plumed, beribboned and spiked, and kept them in a closet hidden behind a bookcase in his home in the La Jolla section of San Diego. He incorporated them into his personal paintings, his advertising work and his books. He even insisted that guests to his home don the most elaborate ones he could find. [...]

As editor in chief of Beginner Books at Random House in the late 1960s, Michael Frith worked closely with Geisel, sometimes into the early hours of the morning. When they were stumped by a word choice, Mr. Frith said, Geisel would often bound to the closet and grab a hat for each of them — a sombrero, or perhaps a fez. There they would be, sitting on the floor, Mr. Frith remembered, “two grown men in stupid hats trying to come up with the right word for a book that had only 50 words in it at most.”

Several of Geisel's hats will be on display a branch of the New York Public Library beginning on Monday.

The first Dr. Seuss book I remember was when my mother read me The 500 Hats of Bartholomew Cubbins. Maybe that was inspired by his collection? Or could the collection be inspired by the book? It came out in 1938.